Energy storage devices such as lithium batteries are the state of the art power sources for many electronic devices due to their high energy density, high power, and long shelf life. However, there is a risk that energy storage devices might release energy accidentally (e.g., through abuse) in an undesirable or uncontrolled manner. Building safety features into batteries can reduce this risk and improve abuse tolerance.
The safety of current lithium-ion batteries may be compromised by various mechanisms, many of which are related through a temperature increase phenomenon. Excessive heat and thermal runaway may occur due to electrolyte decomposition at overcharge and at elevated operating temperatures. Thermal runaway might also occur due to oxygen evolution in case of high voltage cathode materials such as LiCoO2. In some cases, mechanical abuse can also cause active materials to short together, thereby resulting in thermal runaway. This could be caused due to overcharging the batteries, electrical shorts, or mechanical abuse related shorting. A rapid release of heat during chemical reactions pertaining to electrolyte or cathode decomposition can increase the risk of thermal runaway in conventional two-dimensional batteries.
Self-stopping devices, for example polymer or ceramic materials with Positive Temperature Coefficient (PTC) of resistance, have been used to enhance the safety of conventional two-dimensional batteries. Such materials are sometimes referred to as resettable fuses or self-regulating thermostats. For example, reference to P. G. Balakrishnan, R. Ramesh, and T. Prem Kumar, “Safety mechanisms in lithium-ion batteries,” Journal of Power Sources, 2006, 155, 401-414 may help to illustrate the state of the art in safety mechanisms in conventional lithium-ion batteries, and is therefore incorporated by reference as non-essential subject matter herein.
Heat dissipation in a battery should be sufficient to reduce the risk of thermal runaway. However, traditional two-dimensional batteries may not dissipate sufficient heat because too much of the cross sectional area of the battery is taken up by cathode and anode materials, which typically do not conduct heat very well.
Three-dimensional battery architectures (e.g., interdigitated electrode arrays) have been proposed in the literature to provide higher electrode surface area, higher energy and power density, improved battery capacity, and improved active material utilization compared with two-dimensional architectures (e.g., flat and spiral laminates). For example, reference to Long et. al., “Three-dimensional battery architectures,” Chemical Reviews, 2004, 104, 4463-4492, may help to illustrate the state of the art in proposed three-dimensional battery architectures, and is therefore incorporated by reference as non-essential subject matter herein. FIG. 1 shows a schematic representation of a cross-section of one example of a three-dimensional battery that has been proposed in the literature. The battery includes a cathode current collector 10 from which cathodes 11 extend in a height direction at various points. A similar structure is made with an anode current collector 14 and anodes 13. The regions between the cathodes 11 and the anodes 13 (and some areas of the current collectors 10 and 14) include electrolyte 12.
The cathodes 11 and anodes 13 may be assembled in various three-dimensional configurations. This can include, for example, inter-digitated pillars or plates where the anodes 13 and the cathodes 11 are in proximity to each other in more than one direction. For example, in FIG. 1, each anode 13 is in close proximity to two cathodes 11, one on either side. In structures such as pillars, each electrode could be in proximity to surfaces from more than two counter electrodes. The anode and cathode current collectors 10 and 14 can be separate (top and bottom connection as shown in FIG. 1) or co-planar.
However, three-dimensional battery architectures can present challenges for achieving adequate safety. Accordingly, improved safety features for three-dimensional batteries are needed in the art.